smsse.exe not found - PC keeps restarting itself

Hi people
I know this has appeared elsewhere but there seems to be conflicting info in replies. I get the message "smsse.exe not found (blah blah)" message on starting up. At random times, the machine will restart itself. One night I left it running all night and it remained stable the whole time; the next day it did the restart trick while I was working. It's totally unpredictable. Some people say their machines run perfectly fine without smsse.exe; others say that without the session manager, I can expect exactly this problem with random restarting.
I have run Registry Mechanic which logs some problems with some *.dlls. Spyware Doctor tells me I have some problem trojans. There are people out there who say that some trojans bring in or exploit a file called smsse.exe.
Any advice available then? How can I restore smsse.exe for example?
Thanks in advance - I want to sort this problem out before my broadband account comes active as I don't want too many conflicts going on when that starts...
Best regards
DB

Next, run HijackThis and place a tick-mark in the little square before (if still there):
any lines with smsse.exe in it

Now click on the Fix Checked button in HJT.
When done, delete smsse.exe
Delete all files and directories from: C:\Documents and Settings\[username]\Local Settings\Temp
Repeat this for ALL [usernames].
Boot normal. When all OK, switch System Restore back on.